Stereoselective Radical Tandem Cyclohydrostannation of Optically Active Di-unsaturated Esters of TADDOL

Abstract

This paper reports the results obtained in a study on the radical addition of triorganotin hydrides, R 3 SnH (R ) Me, n-Bu, Ph; Neophyl), to four TADDOL unsaturated diesters. It was found that these reactions lead in high yields to products of cyclohydrostannation. It was also found that whereas the addition of these hydrides to TADDOL diacrylate and TADDOL dimethacrylate leads to the expected mixtures of two and four cycloundecane diastereoisomers, respectively, the addition of triphenyltin hydride to TADDOL disubstituted acrylates yields only four out of the 16 possible stereoisomers. The observed high stereoselectivity is consistent with the radical tandem cyclohydrostannation mechanism proposed. Only in the case of the hydrostannation of TADDOL diacrylate with trimethyl-and triphenyltin hydrides could the diastereoisomers obtained in higher proportion (5a and 8a) be isolated in pure form. The subsequent reduction (lithium aluminum hydride) of macrolides 5a and 8a afforded the corresponding optically active diols 26 and 27 in high yield. Full 1 H, 13 C, and 119 Sn NMR data are given.

A New Method for the Stereoselective Synthesis of Macrodiolides From TADDOL Derivatives

“…Similar studies on the hydrostannation of TADDOL di(2-methyl-3-phenyl) 1c and di(2.3diphenyl)acrylates 1d showed that the free radical addition of triphenyltin hydride leads to the same products of ciclohydrostannation reported previously. 1 Substrate 1c showed similar results with the two methods tested but the diasteroselectivities obtained are lower (Method A, D%= 10, 14, 18, 58; and Method B, D%= 16, 16, 14, 56) than the previous report (D%= 6, 10, 13, 71). The best condition was A where the diastereoselectivity obtained is greater than reported (D%= 25, 3, 10, 62).…”

“…So, we decided to study a new procedure for the synthesis of these macrocycles through the radical addition of different triorganotin hydrides, R 3 SnH (R= Me, n-Bu, Ph; Neophyl), to the same unsaturated TADDOL diesters, in THF as solvent 8 and under MW conditions. Based on previous reports, 1 We changed the solvent toluene by THF. Furthermore, the Dielectric Constant (ε´) and Tan (δ) of THF is greater than toluene, due to the better ability of THF to absorb microwave energy.…”

Mono- and diorganotin derivatives of (S)-BINOL diesters as precursors of C₂ symmetry chiral catalysts

“…Our research group has widely studied the hydrostannation reaction over TADDOL diesters 7 with four triorganotin hydrides (R 3 SnH, R= Me, n-Bu, Ph and Neophyl) that occurred with intramolecular cyclization with high yield and diastereoselectivity with no polymerization or diaddition products observed. The observed cyclohydrostannation could be explained assuming that the triorganotin radical will add to the backbone of one of the unsaturated groups, leading to the alkyl radical A (Figure 2), which in turn adds to the less substituted carbon of the other olefinic group, leading to the product of endocyclization, i.e, the radical B.…”

A Tribute to Prof. Julio César Podestá

“…Thus, he has recently started studies on the synthesis of optically active macrolides via a tandem radical cyclohydrostannation of unsaturated TADDOL diesters that proceeds with very high stereoselectivity. 19 He is also interested in the development of more efficient and versatile protocols for carrying out synthesis via cross-coupling reactions. 20 The results obtained by Julio's research group until present have resulted in the publication of 70 research articles and have also been reported in numerous national and international meetings and symposia.…”